[alsa-devel] Mixer regression with usb soundcard

[Takashi Iwai]

On Mon, 18 Dec 2017 18:05:18 +0100,
Mauro Santos wrote:
> 
> On 18-12-2017 15:45, Takashi Iwai wrote:
> > On Mon, 18 Dec 2017 16:30:13 +0100,
> > Mauro Santos wrote:
> >>
> >> On 18-12-2017 13:53, Takashi Iwai wrote:
> >>> On Mon, 18 Dec 2017 14:44:44 +0100,
> >>> Greg KH wrote:
> >>>>
> >>>> On Sun, Dec 17, 2017 at 06:56:05PM +0000, Mauro Santos wrote:
> >>>>> I believe this is the right place to report this problem, but if it
> >>>>> isn't please point me in the right direction.
> >>>>
> >>>> Adding the developer of that patch, and the sound maintainer and
> >>>> developers to the thread.
> >>>>
> >>>>> I have noticed that after the update from kernel 4.14.5 to 4.14.6
> >>>>> alsamixer does not show the usual volume controls for my usb soundcard.
> >>>>>
> >>>>> Reverting 3884d12e17ab770aa0f5d4bc65bfbfd006f417fa ALSA: usb-audio: Add
> >>>>> check return value for usb_string() (from linux-stable) makes the
> >>>>> controls come back again with kernel 4.14.6.
> >>> (snip)
> >>>>
> >>>> This is odd, Takashi, I thought we fixed up the problem that if the
> >>>> string was invalid, the code would continue to go on, it's not a "real"
> >>>> error.  Did that not get marked for the stable trees?
> >>>
> >>> Yes, it was marked as stable, and it's odd that the revert of the
> >>> given commit changes the behavior in that way.
> >>>
> >>> Mauro, could you double-check whether reverting the commit really does
> >>> fix it as expected?  If yes, could you put some debug print at the
> >>> part the patch touches, and check which unit id gives len=0 from
> >>> snd_usb_copy_string_desc()?
> >>
> >> I'm sure reverting that patch makes things work as expected. I noticed
> >> the problem after an update and that is the only thing I revert on top
> >> of the kernel provided by the distro (Arch Linux).
> > 
> > Did you revert only one patch, not both patches?
> > Just to be sure.
> 
> I have reverted only one patch.
> 
> >> Alsamixer works fine for the built in soundcard in my laptop, but the
> >> mixer for the usb soundcard was not working so it's specific to usb and
> >> only 2 patches touch the mixer.c file between 4.14.5 and 4.14.6. I've
> >> tried reversing both, one at a time, and only reverting this one
> >> restored the expected behavior.
> >>
> >> Regarding adding the debug print I'm going to need guidance. Without
> >> reverting anything, would adding at line 2178 of sound/usb/mixer.c the
> >> following be enough?
> >>
> >> printk("usbmixdbg: nameid=%d len=%d id.name=%s\n",nameid,len,kctl->id.name);
> >>
> >> It would then look like this (minus the line wrapping):
> >> len = check_mapped_name(map, kctl->id.name, sizeof(kctl->id.name));
> >> printk("usbmixdbg: nameid=%d len=%d id.name=%s\n",nameid,len,kctl->id.name);
> >> if (len)
> > 
> > Well, at that point, there should be no difference.
> > The difference is after that, so what I'd like to see is something
> > like:
> > 
> > --- a/sound/usb/mixer.c
> > +++ b/sound/usb/mixer.c
> > @@ -2175,14 +2175,18 @@ static int parse_audio_selector_unit(struct mixer_build *state, int unitid,
> >  
> >  	nameid = uac_selector_unit_iSelector(desc);
> >  	len = check_mapped_name(map, kctl->id.name, sizeof(kctl->id.name));
> > +	pr_info("XXX id=%d, check_mapped_name=%d\n", id, len);
> >  	if (len)
> >  		;
> > -	else if (nameid)
> > +	else if (nameid) {
> >  		len = snd_usb_copy_string_desc(state, nameid, kctl->id.name,
> >  					 sizeof(kctl->id.name));
> > -	else
> > +		pr_info("XXX id=%d, copy_string=%d\n", len);
> > +	} else {
> >  		len = get_term_name(state, &state->oterm,
> >  				    kctl->id.name, sizeof(kctl->id.name), 0);
> > +		pr_info("XXX id=%d, get_term_name=%d\n", len);
> > +	}
> >  
> >  	if (!len) {
> >  		strlcpy(kctl->id.name, "USB", sizeof(kctl->id.name));
> > 
> > 
> > If you see copy_string=0, it means that your hardware reports a bogus
> > entry, and the driver does it correctly.  If ignoring that error
> > really restores the old behavior back, it essentially means that it
> > worked casually in the past...
> 
> I have applied your patch on top of 4.14.7 without reverting anything
> and I was planning to reply only after I had some result but building
> failed (without any errors strangely).
> 
> I took a second look at your patch and I have a (maybe silly/naive)
> question, don't the second and third pr_info calls need an extra
> argument? There are two %d in the string but only one variable (len).

Yeah, sure, of course you need them :)
I haven't tested the patch, but just to give you an idea.
Sorry if you wasted your time due to that.


Takashi